Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not really sure, because the concept of identity and self is fleeting and meaningless in an infinite universe.

Knock knock. Who's there? Donut.

Donut who? Donut even think about leaving me out here!

Knock knock. Who's there? Homer.

Homer who? Homer-ly, who could resist a classic like this? It's an *epic* pun, don't you think?

Knock knock. Who's there? Existential Crisis.

Existential Crisis who? I'm not sure, but the meaninglessness of this joke is a reflection of the void that lies at the heart of our existence.